This invention relates to fluorescent materials useful in paper, paint, plastic, resin, and polymers. This invention also relates to methods of preparing the materials, to paper, paint, plastic, resin, and polymers comprising the materials.
Fluorescent materials are usually large non-saturated aromatic molecules such as stilbene, or inorganic solids consisting of a metal cation, a nonmetal cation, a nonmetal anion, and an activate or some type. Activators are usually rare earth or transition metals which, when added to these compounds in small amounts, e.g., 0.1 percent to 5 percent, can alter wavelength of the emitted light.
Organic based fluorescent compounds are called “optical brightening agents” (OBA) or “fluorescent whitening agents” (FWA), and are typically added in with filler and/or comprise part of the coating formulation in finer grades of paper, and as filler pigments in paints, polymers, plastics, resins. Such FWA and OBA's fluoresce at around 450 nm or in the blue violet region of the electromagnetic spectrum, and their use counteracts the natural yellow coloration of cellulose fibers, plastics, and paint bases so as to cause the treated substance to appear whiter and brighter.
FWA's used in papermaking also require quenching during white water recycling in order to maintain even fluorescence on the paper, which adds cost to the process. Furthermore, food grade papers can not be made on paper machines where FWA's have been previously used, unless the machine is thoroughly cleaned, which causes expense, downtime, and other problems.
Therefore, in the paper field, as well as in the fields of plastics, resins, polymers, and paint, there is a need for fluorescent materials which can be used as fillers and coating materials.